Plastic pollution, particularly in the ocean, has unforeseen environmental hazards that could be toxic to many marine organisms. Marine plastic pollution commonly brings to mind large floating water bottles. However, most plastic pollution is composed of tiny plastic fragments and synthetic fibers barely visible to the naked eye. These small plastic particles are collectively called microplastics.

Microplastics are plastic particles generally less than 5 millimeters in size. For reference, the average household drinking straw is about 5 millimeters wide. Two of the most common ways microplastics are directly released into the ocean include cosmetics and washing machine drainage. Some personal care products, such as face washes, contain microbeads, those tiny blue spheres used to exfoliate dead skin cells. Plastic microbeads are washed down the drain and can end up in lakes and the ocean. Likewise, many textiles contain synthetic fibers that are released into the environment when we do laundry. Once in the ocean, microplastics can be ingested by marine critters and have potential toxic effects on the marine food web.

Far away from our bathrooms and Laundromats, in the Arctic Ocean, sea ice formation can scavenge (capture and accumulate) particles such as microplastics from seawater into its crystalline matrix (Figure 1). In fact, irregular shaped objects like microplastics, may even be scavenged more efficiently than other particles, such as diatoms. This means that microplastics are removed from the ocean and trapped into Arctic ice. However, as climate change progresses, and multiyear Arctic sea ice begins to melt, concentrated doses of microplastics could be re-introduced into the ocean- but to what effect?

Obbard et al. explored the distribution of microplastics in the marine environment to identify where microplastics are ending up in the ocean. This study will help identify regions that might be most impacted by microplastics today, as well in the future.

Obbard et al. were not originally looking for microplastics in sea ice. In fact, they were looking for diatoms! They received 3 ice cores from a 2005 NSF-funded project and an additional ice core from a 2010 NASA-funded project to investigate diatom habitats in Arctic sea ice (Figure 2). As Obbard et al. began their study on the first ice core segment, they noticed 24 brightly colored objects which they identified as plastic. Needless to say, these researchers wanted to learn more about what types of plastic and how much was in these Arctic ice cores.

Ice cores were cut into sections of 50-100 cubic centimeters with a band saw, melted, and then filtered so that any particles larger than 22 microns, typical of most microplastics, would be retained. Filtered samples were dried and examined under a microscope as an initial screen for potential microplastics. Subsequently, a technique called Fourier Transform Infrared (FTIR) stereoscopy was used to confirm and categorize particles as plastic by identification of their unique chemical signatures.

The Findings

Microplastics and synthetic particles were found in all four sea ice cores ranging in size from 2 mm fibers to orange chips less just barely retained during the filtration process (~0.02 millimeters). Blue, black, red, and green were the most abundant colored pieces present.

Figure 3: (A) The total number of microplastic pieces per liter of seawater from the melted ice segments according to type of plastic polymer found. Plastics are all identified by using FTIR. (B-F) Photographs of microplastic fragments where scale bar represents 1 mm. (B) polyester, (C) polypropylene, (D) polyester, (E) nylon, and (F) polyethylene.

The concentration of microplastics, and other synthetic particles, ranged from 34 to 234 pieces per cubic meter of ice. This concentration is an order of magnitude higher than seawater microplastic concentrations from the North Atlantic and North Pacific gyre (whose concentrations average 0.34 and 0.12 particles per cubic meter of water, respectively.). This suggests that sea ice concentrates microplastics and could be a global sink for these synthetic particles.

The most abundant synthetic particle found, rayon, is not a plastic, but was so dominant in the sea ice the investigators included it. On average, rayon constituted 54% of the synthetic particles found in sea ice. Rayon is found in cigarette filters and clothing articles and is released into the ocean commonly through sewage effluent. Polyester composed 21% of the remaining synthetic particles, followed by 16% nylon, 3% polypropylene and ≤2% each of polystyrene, acrylic, and polyethylene (Figure 3).

Climate change has caused the thickness of multiyear sea ice to decrease. Using the lowest concentration of synthetic particles found (38 particles per cubic meter of sea ice), sea ice melting could release 1 trillion microplastic particles in the next decade. This additional microplastic and synthetic particle input poses addition risks to ocean critters if they ingest them.

Significance

This study adds to our understanding of where are microplastics going in the ocean, which has been confusing scientists for years. Despite increasing plastic production, the abundance of microplastics in seawater remains mysteriously invariant. This study suggests that microplastics may be scavenged by sea ice, which concentrates microplastic up to 10 times greater compared to sea water. Thus, sea ice may be an important sink for microplastics. Melting sea ice due to climate change threatens to re-release these particles into sea water with unknown consequences to the environment.

I received a Ph.D. in oceanography in 2014 from the Graduate School of Oceanography (URI) and am finishing up a post-doc at the University of Maryland Center for Environmental Science (Horn Point Laboratory). I am now the Research Coordinator for the Delaware National Estuarine Research Reserve.

Carbon is my favorite element and my past times include cooking new vegetarian foods, running, and dressing up my cat!

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